As a conventional center crank eccentrically oscillating speed reducer, there is known a speed reducer having an output portion configured so that pins are embedded at uniform intervals in an inner peripheral part, a camshaft configured to have a gear, to be disposed at a substantially center of the pins of the output portion, and to rotate with respect to the output portion, a toothed disk configured to have external teeth meshing with the pins of the output portion, to engage with the camshaft, and to be eccentrically moved by the camshaft, and a housing configured to have output pins engaging with the toothed disk. Power is transmitted from a motor to the gear of the camshaft (see, e.g., Patent Document 1).
Patent Document 1: JP-A-2000-65162 (pages 2 and 3 and FIG. 1).